Endogenous opiate-like substances (endorphins) have recently been discovered. These substances function both as neurotransmitters and as neuromodulators within the central nervous system. Alterations in the function of endorphin mediated behaviors may play a role in mental illness. We are studying the action of endorphins on mood, memory, hormones, and learning. This Unit has tested the efficacy of narcotic antagonists in the treatment of affective illness and schizophrenia and will be studying the pharmacological and possibly therapeutic effects of beta-endorphin in man.